Method of fabricating special shaped ferrites



Nov. 29, 1960 B. R. EICHBAUM EI'AL 2,961,709

METHOD OF FABRICATING SPECIAL SHAPED FERRITES Filed Dec'. 16, 1957IMPROVED METHOD OF FABRICATING SPECIAL SHAPED FERRITE CORES SPECIALSHAPED FERROSPINEL CORES ADDITIONAL THERMAL TREATMENT AT 1000- 15D0CSPECIAL SHAPED FERROSPIN EL CORE BODY EXHIBITING A RECTANGULARHYSTERESIS LOOP AND SQUARE KNEES INVENTORS BARLANE R. EIOHBAUM ERNEST D.SDHUENZEL BYW AGENT United States Patent METHOD OF FABRHJATING SPECIALSHAPED FERRITES Barlane R. Eichbaum and Ernest'C. Schuenzel,Poughkeepsie, N.Y., assignors to International Business MachinesCorporation, New York, N.Y., a corporation of New York Filed Dec. 16,1957, Ser. No. 702,830 6 Claims. (Cl. 18-475) This invention relates tothose ferromagnetic substances known as ferrospinels and in particularto an improved method of fabricating such materials. More particularly,it relates to a method of improving the magnetic characteristics ofthese materials so as to make them more suitable for use in memory typemechanisms.

The usual method of fabricating ferrites involves compressing the metaloxide powders in a die and plunger to form a solid body of desired shapeand size. The so formed body is then sintered at elevated temperaturesunder suitable atmospheric conditions to form the ferrospinel structureand subsequently cooled to room temperature. However, this processsuffers the disadvantage of requiring special dies for each shape offerrite body desired. Thus, in the past, when odd shaped bodies wereneeded, they were cut to size from a larger ferrite disc with theultrasonic cutter device as described in application Serial No. 431,613,now abandoned, filed on May 21, 1954, by Lloyd P. Hunter and assigned tothe same assignee as the inventor of this application. In general, mosttoroidal shaped ferrites prepared by this method were ultrasonically cutfrom a completely fired ferrite disc. The magnetic properties of theferrite bodies thus prepared have been improved by the ceramic treatmentdescribed herein.

A broad objective of this invention is to provide a convenient method ofmaking special shaped ferrite bodies.

A more specific object of this invention is to improve the magneticcharacteristics of ferrite bodies cut to shape by means of theultrasonic cutting technique.

Among the other objects is to provide an improved method of processingferrospinel materials so as to obtain a more nearly ideal rectangularhysteresis characteristic.

Other objectives will be pointed out in the following description andclaims which disclose by way of example the principle of the inventionand the best mode, which has been contemplated, of applying thatprinciple.

Applicants have discovered that the desirable magnetic characteristicsof a multipath ferrite element compressed into shape with a special dieand plunger could be duplicated with ultrasonic cutting by subjectingthe ferrite body to two thermal treatments, one preceding and the otherfollowing the ultrasonic cutting step.

A preferred method of preparing these bodies according to the practiceof this invention comprises the steps of compressing the ferrite powdersinto a large disc of such a state of compactness as to enable theultrasonic cutter to operate thereon without crumblingthe body, cuttingout a piece of desired shape from the disc and firing the body in thesame manner as would ordinarily be employed in the processing of apressed ferrite core. The cutting may take place on a disc which as beenmerely fired to a rigid state or on a disc which has been fired tocomplete maturity. It is found, however, that the cutting process ismade easier when the unmatured ferrite slab is employed. The effect ofthis treatment on the B-H characteristics of square loop ferrites isillustrated ice 1 by the following data in Tables I and H which comparecores of two ferrite systems made using pressed techniques with thoseusing the ultrasonic cutting and the two stage heating process describedabove.

The accompanying drawing is a flow sheet illustrative of such process.

1 Cadmium-manganese ferrite (20 mol percent (MO, 40 mol percent M110, 40mol percent FeiOa).

Table 11 Code N 0. Sintering Procedure Br/Bs He (oersteds) 301 1 Pressedtoroid-fired l,400 O.-1 hr 0.90 1.0 301A Ultrasonically cut from discfired at 0.88 1. 5

1,400" O. for 1 hr. 301B 301A retired for 2 hrs. at 1,100 O 0.90 1. 35301U Ultrasonlcally cut from disc flred at 0.88 1. 7

1,400 O. for 24 hrs. 301V 301U retired 15% hrs. at; 1,450 O 0.90 0. 530lX. 301V refired 1 hr. at l,450 G 0. 0. 4

1 Magnesium-manganese ferrite (37.5 mol percent MgO, 22.5 mol percentMnO, 40 mol percent F8203).

The data shows that the additional heating step produces a ferritehaving a higher Br/Bs ratio, squarer knees and lower coercive force thanthe untreated ultrasonically cut ferrite body. The results obtainedusing the method of this invention also compare favorably with thoseobtained from die pressed toroids with the single sintering process.

From consideration of the ceramic processes involved, applicants haveconceived the following theoretical explanation for the effectiveness ofthis process. This hypothesis assumes that the ultrasonic cutting steprelieves internal strains in the material in the outer regions of thecore where the cutting has occurred. The present process permits thesestrains in the skin region to develop during the additional period ofheating. Since it is this skin region of the core which plays such animportant role in determining the actual operating characteristics ofthe ferrite, it is observed that the magnetic properties of the bodiesthus treated have improved significantly.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied to a preferredembodiment, it will be understood that various omissions andsubstitutions and changes in the form and details of the deviceillustrated and in its operation may be made by those skilled in the artwithout departing from the spirit of the invention. It is the intentiontherefore to be limited only as indicated by the scope of the followingclaims.

What is claimed is:

1. In a method of making ferrite bodies for computer type mechanismsforming a mixture of Fe O and other selected bivalent metal oxides, diepressing the mixture into a thin disc, heating said disc until itassumes a rigid state, ultrasonically cutting a body of desired shapefrom said disc; the step of thereafter subjecting said body to anadditional thermal treatment at 10001500 C. for 1-24 hours.

2. In a method of making ferrite bodies for computer type mechanismsforming a mixture of cadmium oxide, manganese oxide and ferric oxides;die pressing the mixture into a thin disc; heating said disc until itassumes a shape from said disc; the step of thereafter subjecting saidbody to an additional thermal treatment at 1000- 1500 C. for 1-24 hours.

3. In-a method of making ferritebodies for computer type mechanismsforming a mixture of 20 mol percent CdO, 40 mol percent MnO and 40 molpercent Fe O die pressing the mixture into a thin disc; heating saiddisc at about 800 C. for 30 minutes; ultrasonically cutting a body ofdesired shape from said disc; thestep of thereafter subjecting said bodyto an additional thermal treatment'at about 1200 C. 'for one hour.

4. In a method of making ferrite bodies for computer type mechanismsforming a'mixture of 20 mol percent CdO, 40 mol percent MnO and 40 molpercent Fe O die pressing the mixture into a thin disc; heating saiddisc at about 1200 C. for one hour; ultrasonically cutting a body ofdesired shape from said disc; the step of thereafter subjecting saidbody to an additional thermal treatment at about 1200 C. for onehour.

5. In a method of making ferrite bodies for computer type mecranismsforming a mixture of manganese oxide, magnesium oxide and ferric oxide;die pressing the mixture into a thin disc; heating said disc until itassumes a rigid state; ultrasonically cutting a body of the desiredshape from said disc; the step of thereafter subjecting said body to anadditional thermal treatment at 1000- 1500 C. for 1-24 hours.

6. In a method of making ferrite bodies for computer type mechanismsforming a mixture of 37.5 mol percent MgO, 22.5 mol percent MnO and 40mol percent Fe O die pressing the mixture into a thin disc; heating saiddisc at about 1400 C. for one hour; ultrasonically cutting abody of thedesired shape from said disc; the step of thereafter subjecting saidbody to an additional thermal treatment'at 1100 C..for two hours.

References Cited in the file of this patent UNITED STATES PATENTS

1. IN A METHOD OF MAKING FERRITE BODIED FOR COMPUTER TYPE MECHANISIMS FORMING A MIXTURE OF FE2O3 AND OTHER SELECTED BIVALENT METAL OXIDES, DIE PRESSING THE MIXTURE INTO A THIN DISC, HEATING SAID DIC UNTIL IT ASSUMES A RIGID STATE, ULTRASONICALLY CUTTING A BODY OF DESIRED SHAPE FROM SAID DISC, THE STEP OF THEREAFTER SUBJECTING SAID BODY TO AN ADDITIONAL THERMAL TREATMENT AT 1000-1500*C. FOR 1-24 HOURS. 